openzeppelin-solidity/contracts的代码学习——payment

payment - A collection of smart contracts that can be used to manage payments through escrow arrangements, withdrawals, and claims. Includes support for both single payees and multiple payees.（这个是不是就是token中withdrawl的来源，要好好看看，在博客的the security of smart有写）

临时账户：其实就是一个映射，在下面例子即deposits_，存储某address应该从合约中取出的钱数

下面这里的代码是openzepplin中写的有关实现临时账户的标准，值得学习，我们学习类似cryptopunks的代码的时候就发现他们是这么写的

https://github.com/OpenZeppelin/openzeppelin-solidity/tree/master/contracts/payment

Escrow.sol

pragma solidity ^0.4.23;

import "../math/SafeMath.sol";
import "../ownership/Ownable.sol";


/**
 * @title Escrow
 * @dev Base escrow contract, holds funds destinated to a payee until they
 * withdraw them. The contract that uses the escrow as its payment method
 * should be its owner, and provide public methods redirecting to the escrow's
 * deposit and withdraw.
 */
contract Escrow is Ownable {
  using SafeMath for uint256;

  event Deposited(address indexed payee, uint256 weiAmount);
  event Withdrawn(address indexed payee, uint256 weiAmount);

  mapping(address => uint256) private deposits_;
  //得到临时账户中的余额
  function depositsOf(address _payee) public view returns (uint256) {
    return deposits_[_payee];
  }

  /**
  * @dev Stores the sent amount as credit to be withdrawn.
  * @param _payee The destination address of the funds.
  */
　//往临时账户中存钱，因为声明为payable，所以调用该函数的address通过将msg.value数量的金额传给了合约地址，并同时将数额写到临时账户deposits_上
  function deposit(address _payee) public onlyOwner payable {
    uint256 amount = msg.value;//为什么不直接用msg.value进行add运算，是这样更安全吗？？？？？？
    deposits_[_payee] = deposits_[_payee].add(amount);//为了安全，不使用+来直接运算，而是使用SafeMath.sol中的函数

    emit Deposited(_payee, amount);
  }

  /**
  * @dev Withdraw accumulated balance for a payee.
  * @param _payee The address whose funds will be withdrawn and transferred to.
  */

  //从合约地址中取出临时账户上的所有钱，并将临时账户上的数额清零
  function withdraw(address _payee) public onlyOwner {
    uint256 payment = deposits_[_payee];
    assert(address(this).balance >= payment);//原本是this.balance来得到当前账户地址上的余额？？？？？？，address(this)就是是显示转换成合约地址为address类型

    deposits_[_payee] = 0;

    _payee.transfer(payment);

    emit Withdrawn(_payee, payment);
  }
}

疑惑address(this).balance的解决,(这里的this代表的是合约的地址)：

pragma solidity ^0.4.24;  
contract Get{
//查询当前的余额
  function getBalance() public view returns(uint){
      return this.balance;
  }
  event SendEvent(address to, uint value, bool result);
  //使用send()发送ether，观察会触发fallback函数
  function sendEther() public{
      bool result = this.send(1);
      emit SendEvent(this, 1, result);
}

当想要使用this.balance这么写得到账户的余额时，remix编译中会报警告：

Warning:Using contract member "balance" inherited from the address type is deprecated.Convert the contract to "address" type to access the member,for example use "address(contract).balance" instead.

除此之外，使用this.send也是会报相似的警告：

Warning:Using contract member "send" inherited from the address type is deprecated.Convert the contract to "address" type to access the member,for example use "address(contract).send" instead.

这就是this.balance为什么改为address(this).balance的原因，在这里this.send也要改为address(this).send

PullPayment.sol

pragma solidity ^0.4.24;

import "./Escrow.sol";


/**
 * @title PullPayment
 * @dev Base contract supporting async send for pull payments. Inherit from this
 * contract and use asyncTransfer instead of send or transfer.
 */
contract PullPayment {
  Escrow private escrow;

  constructor() public {
    escrow = new Escrow();
  }

  /**
  * @dev Withdraw accumulated balance, called by payee.
  */
  //取钱
  function withdrawPayments() public {
    address payee = msg.sender;
    escrow.withdraw(payee);
  }

  /**
  * @dev Returns the credit owed to an address.
  * @param _dest The creditor's address.
  */
  //查余额
  function payments(address _dest) public view returns (uint256) {
    return escrow.depositsOf(_dest);
  }

  /**
  * @dev Called by the payer to store the sent amount as credit to be pulled.
  * @param _dest The destination address of the funds.
  * @param _amount The amount to transfer.
  */
  //向临时账户中存钱
  function asyncTransfer(address _dest, uint256 _amount) internal {
    escrow.deposit.value(_amount)(_dest);//形如someAddress.call.value()() ，因为deposit是payable的，value(_amount)相当于{value:_amount}

  }
}

contracts/payment/ConditionalEscrow.sol

就是当某条件允许时才能够将临时账户中的钱取出

该函数为abstract函数

pragma solidity ^0.4.23;

import "./Escrow.sol";


/**
 * @title ConditionalEscrow
 * @dev Base abstract escrow to only allow withdrawal if a condition is met.
 */
contract ConditionalEscrow is Escrow {
  /**
  * @dev Returns whether an address is allowed to withdraw their funds. To be
  * implemented by derived contracts.
  * @param _payee The destination address of the funds.
  */
  function withdrawalAllowed(address _payee) public view returns (bool);

  function withdraw(address _payee) public {
    require(withdrawalAllowed(_payee));//只有满足情况了才能withdraw，下面即实现例子RefundEscrow.sol
    super.withdraw(_payee);
  }
}

contracts/payment/RefundEscrow.sol

当账户状态为Refunding时，存钱的人能把存的钱取回

当账户状态为Closed时，受益人才能把账户中的钱取出

pragma solidity ^0.4.23;

import "./ConditionalEscrow.sol";
import "../ownership/Ownable.sol";


/**
 * @title RefundEscrow
 * @dev Escrow that holds funds for a beneficiary(收益人), deposited from multiple parties.
 * The contract owner may close the deposit period, and allow for either withdrawal
 * by the beneficiary, or refunds to the depositors.
 */
contract RefundEscrow is Ownable, ConditionalEscrow {
  enum State { Active, Refunding, Closed }

  event Closed();
  event RefundsEnabled();

  State public state;
  address public beneficiary;

  /**
   * @dev Constructor.
   * @param _beneficiary The beneficiary of the deposits.
   */
  constructor(address _beneficiary) public {//声明受益人，此时账户状态为Active
    require(_beneficiary != address(0));
    beneficiary = _beneficiary;
    state = State.Active;
  }

  /**
   * @dev Stores funds that may later be refunded.
   * @param _refundee The address funds will be sent to if a refund occurs.
   */
  function deposit(address _refundee) public payable {//往账户存钱
    require(state == State.Active);
    super.deposit(_refundee);//使用的是super，即父合约而不是this本合约
  }

  /**
   * @dev Allows for the beneficiary to withdraw their funds, rejecting
   * further deposits.
   */
  function close() public onlyOwner {//当账户状态为Closed，就不能再往里面存钱了，只能受益人取钱
    require(state == State.Active);
    state = State.Closed;
    emit Closed();
  }

  /**
   * @dev Allows for refunds to take place, rejecting further deposits.
   */
  function enableRefunds() public onlyOwner {
    require(state == State.Active);
    state = State.Refunding;
    emit RefundsEnabled();
  }

  /**
   * @dev Withdraws the beneficiary's funds.
   */
  function beneficiaryWithdraw() public {//受益人取钱
    require(state == State.Closed);
    beneficiary.transfer(address(this).balance);
  }

  /**
   * @dev Returns whether refundees can withdraw their deposits (be refunded).
   */
  function withdrawalAllowed(address _payee) public view returns (bool) {//当账户状态为Refunding时，存钱的人能把存的钱取回
    return state == State.Refunding;
  }
}

contracts/payment/SplitPayment.sol

付款人能够根据自己在该合约生成时付的钱生成的股份shares[payee]占总股份的比例来要求合约返还自己的钱

pragma solidity ^0.4.24;

import "../math/SafeMath.sol";


/**
 * @title SplitPayment
 * @dev Base contract that supports multiple payees claiming funds sent to this contract
 * according to the proportion they own.
 */
contract SplitPayment {
  using SafeMath for uint256;

  uint256 public totalShares = 0;
  uint256 public totalReleased = 0;

  mapping(address => uint256) public shares;//payee所拥有的股份
  mapping(address => uint256) public released;//合约已经还给payee的钱
  address[] public payees;

  /**
   * @dev Constructor
   */
  constructor(address[] _payees, uint256[] _shares) public payable {
    require(_payees.length == _shares.length);
    require(_payees.length > 0);

    for (uint256 i = 0; i < _payees.length; i++) {//在该合约创建的时候_payee就都加到该合约中了，比例也是早就算好的
      _addPayee(_payees[i], _shares[i]);
    }
  }

  /**
   * @dev payable fallback
   */
  function () external payable {}

  /**
   * @dev Claim your share of the balance.
   */
  function claim() public {
    address payee = msg.sender;

    require(shares[payee] > 0);

    uint256 totalReceived = address(this).balance.add(totalReleased);//就是合约还回去的钱totalReleased+现在合约中有的钱 = 合约总共收到的钱
    uint256 payment = totalReceived.mul( //等价于（（totalReceived*（shares[payee]/totalShares））-released[payee]），就是通过比例算出本payee发给该合约的钱-之前还的钱released[payee] = 还需要还的钱payment
      shares[payee]).div(
        totalShares).sub(
          released[payee]
    );

    require(payment != 0);
    assert(address(this).balance >= payment);//合约中现在还有的钱要大于payment才能把钱给payee

    released[payee] = released[payee].add(payment);
    totalReleased = totalReleased.add(payment);

    payee.transfer(payment);
  }

  /**
   * @dev Add a new payee to the contract.
   * @param _payee The address of the payee to add.
   * @param _shares The number of shares owned by the payee.
   */
  function _addPayee(address _payee, uint256 _shares) internal {
    require(_payee != address(0));
    require(_shares > 0);
    require(shares[_payee] == 0);

    payees.push(_payee);
    shares[_payee] = _shares;
    totalShares = totalShares.add(_shares);
  }
}

⚠️：Add a leading underscore to internal and private functions，要在internal and private函数的名字前加下划线